At the beginning of the movie, Sam and Ginger start an account at a Los Angeles bank "under the name of Mr. & Mrs. Tom Collins." Sam deposits $2MM (in case of emergency) in a safety deposit box, then gives Ginger the only key.

At the end of the movie, when the whole relationship goes sour, Ginger steals the key out of Sam's desk when the Las Vegas police escort her into the house to get a few things. Minutes later, she arrives at the bank to get the money out of the deposit box, closely pursued by the Las Vegas police who actually help her put the money in bags. The time lapse of a 4-6 hour drive from Vegas to LA isn't even suggested, and of course the presence of the Las Vegas police at both the Rothstein's house and the bank (why would Vegas police have jurisdiction in LA?) prove the slip-up.